The purpose of this project is to biochemically and immunologically characterize type C RNA viruses in order to understand the mechanisms by which these viruses transform cells. Another goal of this research is to determine whether or not these viruses play a role in the etiology of human cancers. Studies currently in progress are the following: 1) Biochemical characterization of new isolates of type C viruses; 2) Studies of the cellular control of endogenous viral gene expression in normal and malignant cells: 3) Search for the presence of type C viral genes and gene products in human tumors; 4) Biochemical characterization of mammalian transforming viruses . BIBLIOGRAPHIC REFERENCES: Ablashi, D. V., Oie, H. K., Armstrong, G. R., Didier-Fichet, M. L., Tronick, S. R., Heine, V. and Dalton, A. J.: Xenotropic properties of an isolate from murine Rauscher leukemia virus. J. Med. Primatol. 5: 223-236, 1976. Tronick, S. R., Golub, M. M., Stephenson, J. R. and Aaronson, S. A.: Distribution and expression in mammals of genes related to an endogenous type C RNA virus of Odocoileus hemionus. J. Virol. (In press, 1977).